Recently, an EL device using electroluminescence (EL) has been developed. The EL device consumes lower power compared to a cathode-ray tube. Further, since the EL device is a self-luminescent device, there are some other advantages, for example, a view angle wider than that of liquid crystal display (LCD), so that progress thereof in the future is expected.
However, since the EL device is vulnerable to moisture, light-emitting luminance may be decreased due to moisture permeating through a defective part of the device or a non-emitting area called “dark spot” can be formed. Therefore, a sealing film having moisture permeability resistance is formed on a surface of the EL device. As the sealing film requiring a low-temperature process as performed on the EL device and very high moisture permeability resistance, an inorganic layer such as a silicon nitride layer and an aluminum oxide layer has been used. Further, there is suggested a sealing film having a stacked structure of an inorganic layer and an organic layer such as UV curable resin (for example, Patent Documents 1 to 3).    Patent Document 1: Japanese Patent Laid-open Publication No. H10-312883    Patent Document 2: Japanese Patent Laid-open Publication No. H04-267097    Patent Document 3: Japanese Patent Laid-open Publication No. S64-041192
However, in order to obtain moisture permeability resistance, a sealing film needs to be formed of a thick inorganic layer capable of burying impurity particles adhering to a substrate surface through a low-temperature process. If a sealing film is formed of a thin inorganic layer that cannot bury impurity particles, a defective part can be formed between the impurity particles and the inorganic layer, and moisture may permeate through the defective part. For this reason, it takes several hours to form a thick sealing film. Even if the sealing film is formed of the thick inorganic layer capable of burying impurity particles, there may be some defective parts. By way of example, if an impurity particle has a protruding part along a direction of a substrate surface, there is a part on which an inorganic layer cannot be deposited due to the protruding part, and, thus, a defective part can be formed.
Further, Patent Document 1 describes a method including forming a buffer layer made of photo curable resin on the EL device and curing the buffer layer to further form an inorganic layer on the buffer layer. However, there is a problem in that the EL device is deteriorated by UV rays irradiated when curing the buffer layer.
Furthermore, Patent Document 2 describes a method including forming an inorganic layer on the EL device and forming a photo curable resin layer on the inorganic layer. In order to obtain high moisture permeability resistance, the inorganic layer needs to be thick enough to bury impurity particles adhering to a glass substrate. Therefore, a time required for forming a sealing film cannot be reduced.
Moreover, Patent Document 3 describes a method including forming an inorganic layer, an organic layer, and an inorganic layer in sequence on the EL device. Even if this method for stacking respective layers is used, if impurity particles adhere to a glass substrate, there may be formed a defective part through which moisture permeate. Therefore, if the inorganic layer is not thick enough, high moisture permeability resistance cannot be obtained.